3,3′-[1,2-Phenylenebis(methylene)]bis(1-ethylbenzimidazolium) dibromide

In the title molecular salt, C26H28N4 2+·2Br−, the central benzene ring makes dihedral angles of 76.75 (11) and 82.40 (10)° with the pendant benzimidazole rings. The corresponding angle between the benzimidazole rings is 57.03 (9)°. In the crystal, the cations and anions are linked via C—H⋯Br hydrogen bonds, forming sheets lying parallel to the bc plane. The crystal structure also features weak C—H⋯π interactions.

In the title molecular salt, C 26 H 28 N 4 2+ Á2Br À , the central benzene ring makes dihedral angles of 76.75 (11) and 82.40 (10) with the pendant benzimidazole rings. The corresponding angle between the benzimidazole rings is 57.03 (9) . In the crystal, the cations and anions are linked via C-HÁ Á ÁBr hydrogen bonds, forming sheets lying parallel to the bc plane. The crystal structure also features weak C-HÁ Á Á interactions.   Table 1 Hydrogen-bond geometry (Å , ).

Related literature
Cg4 is the centroid of the C11-C16 ring.  In the crystal (Fig. 2), the cations and anions are linked via C-H···Br (Table 1) hydrogen bonds, forming twodimensional networks lying parallel to the the bc-plane. The crystal structure also features weak C-H···π interactions involving the centroid of the phenyl (C11-C16) ring.

Experimental
A mixture of benzimidazole (2.36 g, 20 mmol) and finely ground potassium hydroxide (2.36 g, 30 mmol) in 30 ml of DMSO was stirred at room temperature (27-28 °C) for 30 min. 1-Bromoethane (1.50 ml, 20 mmol) was added drop wise in this consistently stirring mixture and further stirred for 2 h at same temperature, poured into water (300 ml) and was extracted by chloroform (5 × 20 ml). The extract was dried by magnesium sulphate and evaporated under reduced pressure to get N-ethylbenzimidazole as a thick yellowish fluid (2.52 g, 86.30%). Furthermore, a mixture of 1 (1.46 g, 10 mmol) and 1,2-bis(bromomethyl)benzene (1.32 g, 5 mmol) in dioxane (30 ml) was refluxed at 110 °C for 18 h. Desired compound (2.2Br) appeared as beige-colored precipitates in dark brown solution. The mixture was filtered and precipitates were washed by fresh dioxane (3 × 5 ml), dried at room temperature for 24 h, and soft lumps so obtained were ground to fine powder (2.40 g, 86.33%). Saturated solution of 2.2Br in methanol (0.5 ml) was exposed to diethyl ether vapours (vapour diffusion) at room temperature overnight to get colourless blocks of (I).

Refinement
All hydrogen atoms were positioned geometrically [C-H = 0.93-0.97 Å] and were refined using a riding model, with U iso (H) = 1.2 or 1.5 U eq (C). A rotating group model was applied to the methyl groups. 3727 Friedel pairs were used to determine the absolute structure. One outliner, (4 0 -4), was omitted in the final refinement.   The crystal packing of the title compound.  (6) Special details Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq